In Selenium IDE, how to get the value of the base url

You can also open your base page and use storeLocation to put the current location into a variable:

|open|/||
|storeLocation|host||
|assertLocation|${host}somepage.html

Bonus: here's how I figured out the corresponding SSL url

|storeEval|window.document.location.toString().replace(new RegExp("^http://([^:]+):80"), "https://$1:40");|hostSSL|

Try this

storeEval|window.document.domain|host
assertLocation|http://${host}/some-page|